Coated articles including low-E coatings are known in the art. For example, see U.S. 2004/0180214, 2004/0005467, 2003/0150711 and 2004/0121165, the disclosures of which are hereby incorporated herein by reference. Low-E coatings typically include one or more IR reflecting layers of a material such as silver or the like. It is known to sputter-deposit a silver IR reflecting layer on and contacting a contact layer of zinc oxide (e.g., see 2003/0150711 and 2004/0121165).
IR reflecting layers such as silver layers are typically deposited by sputtering a silver target in an atmosphere of argon (Ar) gas. This argon atmosphere is used to deposit an IR reflecting layer in a manner so as to reduce any possible oxidation of the same. Oxidation of the silver IR reflecting layer is often viewed as undesirable in that it can sometimes lead to failure and/or undesirable changing of the characteristics of the IR reflecting layer. In an effort to reduce oxidation of silver IR reflecting layers, metal contact layers such as NiCr, Ti or the like are often deposited immediately over silver IR reflecting layers; this may help to reduce oxidation of the silver layer when a further metal oxide layer is sputter-deposited over the metal contact layer of NiCr, Ti or the like. However, the use of metal contact layers is not always desirable, in that they tend to lead to decreased transmission of the coated article and/or significant changes in appearance upon heat treatment such as thermal tempering.
It is also known in the art to use zinc oxide as a contact layer immediately adjacent silver. The traditional way to sputter-deposit zinc oxide in the manufacture of coated articles is to sputter a Zn based metal (or metal alloy) target in an atmosphere saturated with oxygen gas. However, the large amounts of oxygen gas used in traditional sputtering of metal Zn inclusive targets may have a negative impact on the silver which is adjacent the zinc oxide. In particular, due to the use of large amounts of oxygen gas in sputtering zinc adjacent silver, oxygen gas may tend to leak from the zinc sputtering chamber into the adjacent silver sputtering chamber or bay thereby leading to undesirable oxidation of the silver IR reflecting layer. Another possible problem is that a surface of the silver layer may be exposed to oxygen gas as the coating enters and begins to pass through the zinc sputtering chamber. The existence of oxygen tends to degrade silver IR reflecting layers by forming AgO which has a high absorption in the visible spectrum and low reflecting in the IR spectrum. This undesirable phenomenon is particularly detrimental for low-E coatings having thin silver layer such as less than about 150 Å thick.
In order to address the aforesaid problem, it is known to use a ceramic target (or ceramic cathode) to sputter-deposit a zinc oxide contact layer above and contacting a silver IR reflecting layer. For instance, a ZnO target (which is a ceramic target) may be doped with a material such as Al, and sputtered in order to form such a zinc oxide based layer over an IR reflecting layer. The Al is provided in the target in order to make the target conductive enough for efficient sputtering. Ceramic ZnO targets are desirable in that to form a zinc oxide layer which a particular stoichiometry, less oxygen gas is needed in the sputtering atmosphere around the ceramic target because oxygen is already present in the target itself; thereby reducing the likelihood of the adjacent silver IR reflecting layer being damaged by oxygen gas used in sputtering a zinc oxide contact layer. However, it is sometimes not desirable to dope ceramic targets with a metal such as Al, since the Al tends to end up in the deposited layer in significant amounts which may not be desired in certain situations. Unfortunately, if a stoichiometric ZnO target (i.e., ZnOx, where x=1) is not so doped, its conductivity is less than what is needed for efficient sputtering.
In view of the above, it will be apparent that there exists a need in the art for an improved technique for forming zinc oxide inclusive layers, especially adjacent and contacting IR reflecting layers such as silver.
It has been found that the use of a substoichiometric zinc oxide ceramic target is advantageous in this regard. According to certain example embodiments of this invention, a substoichiometric ceramic target comprising ZnOx (e.g., where 0.25≦x≦0.99, more preferably 0.50≦x≦0.97, and even more preferably 0.70≦x≦0.96) is used in sputter-depositing a zinc oxide inclusive contact layer which is located, or is to be located, adjacent and contacting an IR reflecting layer of silver or the like (substoichiometric means that “x” is less than 1.0 in the case of ZnOx).
According to certain example embodiments of this invention, the substoichiometric nature of the ZnOx inclusive ceramic target causes the ceramic target to be more conductive, thereby reducing or eliminating the need for metal dopant(s) in the target. In particular, with no metal doping, a substoichiometric ZnOx inclusive ceramic target is able to realize improved sputtering yields and faster sputtering rates compared to a stoichiometric ZnO ceramic target. This is highly advantageous as will be appreciated by those of skill in the art. In certain example embodiments of this invention, no dopants are needed for a substoichiometric ZnOx inclusive ceramic target.
In certain example embodiments of this invention, a substoichiometric ZnOx inclusive ceramic target may be doped with a non-metal such as F and/or B. F and/or B when used as dopants increase the electrical conductivity of the target, which may be needed in certain situations where x is close to 1.0 even while the target is still slightly substoichiometric. In certain example embodiments of this invention, the target may be doped so as to include from about 0.5 to 5.0% F and/or B, more preferably from about 0.5 to 3% F and/or B (atomic %). In certain alternative embodiments of this invention, a stoichiometric ZnO ceramic target may be doped with from about 0.5 to 5.0% F and/or B, more preferably from about 0.5 to 3% F and/or B.
Such ceramic zinc oxide/suboxide sputtering targets may be used to sputter-deposit ZnO layers in low oxygen environments (i.e., a low amount of oxygen gas is required in the sputtering chamber or bay where the target(s) is located) using either AC or DC sputtering. In certain example embodiments of this invention, no more than about 40%, more preferably no more than about 30%, and most preferably no more than about 20% of the total gas in the sputtering chamber including the ceramic target is oxygen; the remainder of the gas in the sputtering chamber may be argon or the like. Due to the low percentage of O2 gas, the degradation of silver properties can be reduced and/or avoided when the zinc oxide is formed adjacent and contacting a silver based layer.
In certain example embodiments of this invention, there is provided a method of making a coated article including a coating supported by a glass substrate, the method comprising: depositing an infrared (IR) reflecting layer on the substrate; sputtering a ceramic target comprising zinc oxide in forming a first layer comprising zinc oxide on the substrate, where the layer comprising zinc oxide directly contacts the IR reflecting layer and is located above or below the IR reflecting layer; and wherein the zinc oxide of the ceramic target is substoichiometric.
In other example embodiments of this invention, there is provided a method of making a coated article including a coating supported by a glass substrate, the method comprising: depositing an infrared (IR) reflecting layer on the substrate; sputtering a target comprising zinc oxide in forming a first layer comprising zinc oxide on the substrate, where the layer comprising zinc oxide directly contacts the IR reflecting layer and is located above or below the IR reflecting layer; and wherein the zinc oxide of the target is doped with from about 0.5 to 5.0% fluorine. In such fluorine inclusive embodiments, the ceramic target may or may not be substoichiometric.
In still further example embodiments of this invention, there is provided a method of making a coated article including a coating supported by a glass substrate, the method comprising: depositing an infrared (IR) reflecting layer on the substrate; sputtering a target comprising zinc in forming a first layer comprising zinc oxide on the substrate, where the layer comprising zinc oxide directly contacts the IR reflecting layer and is located above or below the IR reflecting layer; and wherein the target comprising zinc is doped with boron. In such boron inclusive embodiments, the target may or may not be stoichiometric, and the target may or may not be ceramic.
In still further example embodiments of this invention, there is provided a sputtering target comprising a material to be sputtered from the target, the material comprising one or more of: (a) substoichiometric zinc oxide; (b) zinc, or zinc oxide, doped with boron; and (c) zinc oxide doped with from about 0.5 to 5.0% fluorine.
In still further example embodiments of this invention, there is provided a coated article comprising a multi-layer coating supported by a glass substrate, the coating comprising: at least one IR reflecting layer comprising silver; a layer comprising zinc oxide located above or below the IR reflecting layer, wherein the layer comprising zinc oxide directly contacts the IR reflecting layer; and wherein the layer comprising zinc oxide is doped with one or more of: (a) from about 0.5 to 5.0% fluorine, (b) from about 0.5 to 10.0% boron. Another similar layer comprising zinc oxide doped with F and/or B may be located on the other side of the IR reflecting layer, and/or adjacent and contacting another IR reflecting layer.